The present invention is related to lock detectors for High Speed Phase Lock Loops of the type employed in quadrature phase shift key (QPSK) receivers. More particular, the present invention relates to lock detectors that employ low cost components and produce higher signal to noise phase locked indication signals than circuit employed heretofore.
2. Description of the Prior Art
The state of the prior art QPSK phase lock detectors will be described in more detail in the description of the prior art drawings. The prior art includes Costas type signal tracking loops which includes hard limiters, analog multipliers and square law multipliers.
The problem with such low speed prior art lock detectors is that they produce low signal to noise phase locked indication signals which are susceptible to generation of false locked signals.
It would be desirable to provide a phase lock detection circuit which comprises high speed and low cost components which generate a higher signal to noise ratio phase locked indication signal than circuits employed heretofore to eliminate false locked signals.